1. Field of the Invention
The present invention relates to a digital information reproduction apparatus by which fast-forward reproduction of digital information compressed and stored can be performed. Particularly, the digital information to be reproduced includes music data and graphics data.
2. Description of the Related Art
With a fast-forward reproduction apparatus stored in a storage medium, such as a minidisk (MD), normally, digital information is intermittently expanded and reproduced so that the fast-forward reproduction is performed. Specifically, frames of data are intermittently retrieved by a host processor from the storage medium, the intermittently retrieved frames of data are serially decoded by a decoder, and reproduced so that the fast-forward reproduction is performed. This method is adopted because of the fact that when the digital data in the storage medium is to be reproduced continuously at a high speed, the data rate becomes so much larger than that of standard reproduction that expansion processing (decoding) cannot follow the high speed. Accordingly, with such fast-forward reproduction, the reproduced information is discontinuous.
Digital-information compression methods include a method, such as a TwinVQ (Transformed Weighted Interleave Vector Quantization) method developed at the HI laboratory of NTT, which utilizes a predetermined parameter obtained in compression of a frame of data to compress the following frame of data. With such a method, decoding of a frame of data needs to be performed in accordance with the aforementioned parameter obtained from the previous frame of data.
The TwinVQ method uses parameters, each of which represents a spectrum envelope, averaged so as to be used for plural frames of data. An LCP parameter, which is called an LSP, is one of the parameters as described above. However, not only the LPC parameter, but other parameters directly representing the spectrum envelope are also used.
As described above, normal fast-forward reproduction of digital information such as that compressed by the TwinVQ method cannot be performed with a simple intermittent reproduction method. For example, with the TwinVQ method, for compression of a frame of data, a parameter obtained in the compression of two immediately-previous frames is used; therefore, for normally decoding a frame of data, a parameter obtained from two immediately-previous frames of data is required.
For example, for fast-forward reproduction at a rate of one frame out of ten frames, in the same method as in the case of the CD, suppose frames of data be retrieved by a host processor at the above rate and the frames thereby retrieved are serially decoded by a decoder. In this case, as shown in FIG. 7, for decoding a frame F21, a parameter obtained from two immediately-previous frames (F1 and F11) decoded is used. In this way, for normally decoding frame F21, a parameter obtained from frames F19 and F20 is in fact required.
Because of these facts, with a reproduction method such as that described above, normal fast-forward reproduction of the digital information compressed by the TwinVQ method cannot be performed.
In consideration of the aforementioned situation, the present invention aims to provide a digital information reproduction apparatus with which a parameter obtained in compression of a frame of data is utilized to compress the following frame of data, by which the fast-forward reproduction that intermittently reproduces the digital information can be implemented.
In another aspect of the situation, for high-speed reproduction, such as the fast-forward reproduction, a selected section is required to sufficiently represent characteristics of audio data; otherwise, the user will have a difficulty in grasping parts for which the fast-forward reproduction are performed. However, when the reproduction is repeated at a predetermined interval of an n section, sections sufficiently representing the audio-data characteristics are not always assured to be the selections.
For elimination of these problems with the conventional techniques, the present invention aims to modify the conventional reproduction apparatus so as to provide an improved reproduction apparatus. With the improved apparatus of this invention, a section reproduced in high-speed reproduction, such as fast-forward or fast-backward reproduction, is selected according to the audio-data characteristics so that the user can grasp the reproduced part.
To these ends, according to one aspect of the present invention, a digital information reproduction apparatus is provided, which comprises storing means storing digital data on a frame basis which is compressed according to a predetermined compression method; reading means to read the compressed digital data stored in the storing means; parameter-calculating means to calculate a compression parameter value on the frame basis, which has been used in the compression of the digital data read out by the reading means; decoding operation means to decode the compressed digital data read by the reading means, the decoding operation means using the compression parameter value calculated in a decoding operation by the parameter-calculation means; reproduction-target-frame selecting means to intermittently perform selection of a reproduction-target frame among a plurality of the frames stored in the storing means, the selection being performed when a command for a fast-forward or fast-backward operation is issued; parameter-calculation-target-frame selecting means to select a calculation-target frame of the compression parameter value required for the fast-forward or fast-backward operation; and fast-reproduction controlling means to allow the parameter-calculating means to calculate the compression parameter value of the parameter-calculation-target frame selected by the parameter-calculation-target-frame selecting means and to allow the decoding operation to be performed to decode the digital data of the reproduction-target frame selected by the reproduction-target-frame selecting means.
In the digital information reproduction apparatus, the frames may be arranged to have a time-series configuration.
Furthermore, for decoding reproduction to be performed by intermittent selection in the fast-forward reproduction, a frame may be arranged to be selected only for parameter-calculation, not for the reproduction.
The term xe2x80x9ccompression parametersxe2x80x9d used herein refers to parameters that have been used in compression of the digital data. The compression parameters are related to frames other than those to be reproduced, but they can be used for accurate decoding and appropriate selection of reproduction-target frames. For example, the compression parameters are required for decoding of other frames than those to be reproduced, the proper compression parameters are used to allow appropriate fast-forward reproduction. Further, use of these compression parameters allows selection of a target frame for intermittent reproduction.
In connection with these compressed parameters, a notable case can be seen in that when the predetermined compression method is to use the compressed parameter value of the predetermined previous frame to decode one of the frames. In such a case, selection of a reproduction-target frame and the predetermined previous frame allows the reproduction-target frame of data to be decoded and reproduced accurately.
When data to be used is sound-data and a compression method uses compression data including a parameter that represents a spectrum envelope, the parameter representing the spectrum envelope is one of the compression parameters described above.
For a compression method such as that described above, a TwinVQ method is frequently used. In this TwinVQ method, LPC parameters are used as the aforementioned compression parameters.
For a selection method of the reproduction-target-frame selecting means, a method to select reproduction-target frames arranged in time series at identical pitches can be considered to be adaptable.
According to another aspect of the present invention, the digital information reproduction apparatus further comprises a frame-feature index extracting means to calculate a feature index of each frame by using the compression parameter value output by the parameter-calculating means on the basis of a frame selected by the parameter-calculation-target-frame selecting means, in which when the command of the fast-forward operation is issued, the parameter-calculation-target-frame selecting means selects a predetermined number of frames following the immediate-previous frame reproduced, and the reproduction-target-frame selecting means selects the next reproduction-target frame in accordance with the feature indexes of plural frames which have been calculated by the frame-feature index extracting means.
In this digital information reproduction apparatus, it is preferable that a frame be selected, as the next reproduction-target frame, which is the most different in the feature index from the immediately-previous frame reproduced or which largely varies in the feature index.
For the feature index, an arrangement is preferably made such as that when the digital data is sound-data and the compression method provides compressed data that comprises a parameter representing at least one item of a spectrum envelope, sound power, pitch, and window size, the feature index is output by use of a parameter value included in the compressed data. Particularly, when the compression method is a TwinVQ method, the feature index is preferably arranged to be output by use of LPC parameters. It is further preferable that, in addition to the LPC parameters, parameters related to an item such as sound power or pitch.
With the apparatus having an arrangement as described above, even when high-speed reproduction such as fast-forward reproduction of audio data, for example, is performed, a reproduction frame can be selected according to the audio-data feature index so as to allow the listener to easily grasp a reproduced part. The listener will be able to grasp the reproduced part more easily when an arrangement is made such that a section is selected, as the next reproduction-target frame, which varies in the feature index, such as a frame which is the most different in the feature index from the immediately-previous frame reproduced.
Another modification is described here, which may be applied to the digital information reproduction apparatus in accordance with the present invention. That is, the same operation device may be arranged to be used to perform the following two operations. One operation is to calculate a parameter value on a frame basis which has been used in compression of the digital data, and another operation is to decode compressed digital data by using a predetermined compression parameter value.
Alternatively of the above, an arrangement may be such that the fast-reproduction controlling means sends out the compressed digital data to the operation device and concurrently, sends out to the operation device an control signal which identifies whether the frame is a reproduction-target frame or a parameter-calculation-target frame.
According to an apparatus arranged as described above, the operation device does not need to recognize whether the reproduction to be performed is the fast-forward reproduction or the standard reproduction, and the processing can be performed by reference to the control signal; by which the entire apparatus can be simplified.
Furthermore, the digital information reproduction apparatus according to the present invention may be arranged to comprise an inverted-reproduction mode to perform reproduction in a sequence opposite to a time-series direction.